The orbital servicing concepts developed for several existing and planned spacecraft are reviewed to illustrate the evolution and capabilities of Shuttle-based support services, and the potential range of future services are categorized by several criteria including transportation systems requirements, supporting facilities and equipment options, and servicing locations. Implications of Space Station-basing the services are described, along with possible implementing systems. In particular, the technique of "formation flying" by means of which spacecraft may be physically isolated from each other while maintaining reasonable propellant requirements for maneuvers between them is explored by representative examples. OTV mission support is described as an evolutionary augmentation of the basic Space Station services.